In recent years, systems that adopt microcells (e.g., PHS (Personal Handyphone System) in Japan) of digital mobile communication systems have been put into practical applications.
In such system using microcells, the size of the area covered by one base station is as small as a radius of 100 to 200 meters, and the subscriber accommodation capability is improved by increasing the frequency reuse efficiency.
The above-mentioned system includes a public system built to cover a wider area including a public area by connecting to a public digital network, and a private system built in home, an office, or the like to have a private branch exchange as a core. In the public system, a plurality of service providers can provide services in a single area.
FIG. 1 shows an example of the basic arrangement of the conventional public system. More specifically, a plurality of base stations CS1 to CSm are distributed in a service area, and respectively form radio zones called cells (microcells) each having a radius of 100 to 200 meters. The base stations CS1 to CSm are connected to a public digital network INS comprising, e.g., an integrated services digital network (to be abbreviated as an ISDN hereinafter).
As a connection interface for the public digital network INW, an I' interface is used. The I' interface is one obtained by adding the position registration procedure of a mobile station to an I interface as a user network interface of the ISDN, and uses two basic interface lines (2B+D) of the ISDN. More specifically, the I' interface has two D channels for control, and four B channels for information communications.
Mobile stations PS1 to PSn are selectively connected to the base stations CS1 to CSm via radio channels in the radio zones formed by the base stations CS1 to CSm, and are connected from the base stations CS1 to CSm to wired telephones TEL1 to TELk or a home system via the ISDN or the ISDN and a subscriber's telephone network SNW.
The public system comprises a management control apparatus CC having a database for operating this system, a customer information management database, and the like. The management control apparatus CC acquires information associated with the mobile stations PS1 to PSn and the base stations CS1 to CSm via the ISDN and a packet network PNW, and performs service management control such as authentication, charging, network management, and the like on the basis of the acquired information.
However, the above-mentioned system suffers the following problems. That is, since the above-mentioned system adopts a microcell system in which each cell has a small radius, high frequency use efficiency is assured but a huge number of base stations must be equipped. For example, when the metropolitan area is a service area, 20 to 40 thousand base stations must be equipped. In an area with a high traffic density like in the metropolitan area, even when a plurality of service providers equip such many base stations, use demands that can offset such investment are assured and may pay economically. However, in an area with a low traffic density like in the provinces or suburbs, not so many use demands are assured. For this reason, it is very uneconomical to equip base stations in units of service providers.
On the other hand, in public spaces such as department stores, underground markets, station yards, and the like, base station groups must be equipped to build private systems for employees who work there, and base stations for the public system must be equipped for general subscribers who visit there. However, as described above, in the current system, since the respective systems operate independently, base stations for both the private and public systems must be equipped, and in some cases, a plurality of base stations for the private and public systems must be equipped at identical positions. Therefore, such multiple systems are very unpreferable since not only they are uneconomical but also they pose another problem, e.g., they spoil the appearances of the sales floors of the department store.